This invention relates to measuring the spectral radiance of a multiplicity of targets and storing the measurement data. In particular the invention is directed to spectroradiometric apparatus and a method whereby an optical system is controlled by a dedicated computer to automatically measure and store spectral radiance data over a wide range of wavelengths for any given target and to automatically scan a number of targets.
Spectroradiometers are used to analyze the spectral content of radiation emanating from a given region or target. They serve to separate light incident from the target into its spectral components and then detect and record this information for analysis.
Measurements of the spectral radiance of a given field of view can be used to determine visual range through the atmosphere. This range can be quantified by measuring the spectral radiance of the sky just above the horizon and that of a terrain feature immediately below and then contrasting these measurements. Spectral radiance measurements can also reveal the atmospheric composition of a given region.
In the prior art, measurements of spectral radiance have only been accomplished by using bulky and cumbersome equipment with great power requirements. All equipment is stationed in the field during use and requires transportation, or at least field readjustment, to alter the target area under analysis.
A by-product of this lack of versatility among prior art systems is inconsistency of spectral radiance measurements.
In U.S. Pat. No. 4,329,050 (Olsen), there is disclosed a spectroradiometer for gathering data along an entire narrow line of a two-dimensional field of view simultaneously. An array of charge coupled devices serves as a detector. The spectroradiometer monitors a region of the earth from an aircraft or spaceship.
This device does not provide for selection of a particular wavelength or wavelengths to be analyzed. It also scans a narrow line rather than a multiplicity of targets.
In U.S. Pat. No. 3,985,442 (Smith), there is disclosed a data acquisition system for a spectrophotometer employing a diffraction grating sequentially moved to a plurality of test positions. This system is to be used in the spectral analysis of materials, particularly luminescent materials, rather than the analysis of the visual range or composition of the atmosphere. It makes no provision for target scanning.
Thus in the prior art there does not exist the apparatus or method for automatically analyzing spectral radiance over a wide range of wavelengths for a multiplicity of targets. Such an apparatus or method can yield consistent measurements and maximize ease of operation.